Redox properties of a viologen-impregnated poly(methyl methacrylate) thin film formed on a water surface

A thin poly(methyl methacrylate) (PMMA) film incorporating a hydrophobic viologen was prepared on a water surface. The film thickness was about 60 nm. Cyclic voltammetric measurements of the film were carried out by putting the film on the surface of an ITO electrode. Clear one-electron redox couples due to one- and two-electron reduction of the viologen were observed. The relationship between the peak current and the scan rate indicated that the viologen was confined to be inside the film. Two sheets of the films were put on the surfaces of a glass substrate; this film assembly was then immersed into an aqueous solution containing Ru(bpy)₃²⁺ and a sacrificial reagent. Visible-light illumination of the film assembly resulted in the appearance of characteristic absorption bands due to one-electron reduced viologen. From a comparison with luminescence quenching experiments of Ru(bpy)₃²⁺ in solution , the interfacial electrontransfer between the photoexcited Ru(bpy)₃²⁺ and the viologen was verified. The results demonstrate a redox-active thin PMMA film.